PTEN gene is localized on chromosome 10q23.3 and identified as a tumor suppressor (non-patent documents 1 and 2). PTEN protein is widely expressed in the cells of the whole body and is known as an enzyme that catalyzes the dephosphorylation reaction of an inositol phospholipid, i.e., phosphatidylinositol 3,4,5-triphosphate (PIP3). PIP3 is synthesized in a cell by P13 kinase (P13K) and causes the activation of protein kinase B(PKB)/AKT. It is said that PTEN is responsible for this dephosphorylation reaction of PIP3 and has a function to convert PIP3 into phosphatidylinositol 4,5-bisphosphate (PIP2).
As mentioned above, PTEN negatively regulates the P13K/AKT signaling pathway (non-patent document 3). Conversely, when the activity of PTEN is inhibited, PIP3 accumulates in cells, thereby the P13K/AKT signaling pathway is activated. It is suggested that the constant activation of the P13K/AKT signaling pathway is involved in diabetes, autism, and some cancers (patent document 4). In addition, molecular modification of PTEN has been known to change its activity (non-patent documents 5 and 6). It is important to maintain the activity of PTEN for diagnosis and therapy of various diseases.